Process of making heat-sealable oriented web

ABSTRACT

A heat-sealable oriented film or layer of a semi-crystalline thermoplastic polymer. The film has a thin, heat-sealable layer of the same thermoplastic polymer having a different heat-seal temperature, which layer is heat-sealable without requiring fusion of the entire film. There is also provided a method for producing the claimed heat-sealable film.

BACKGROUND AND FIELD OF THE INVENTION

The present invention relates to a process of forming a thin,heat-sealable layer on an oriented web.

The use of oriented films and fibers is widespread, particularly withsemi-crystalline thermoplastic polymers. These oriented products arecharacterized by high tensile strength and high modulus. Orientationalso influences crystalline order and hence the melting or softeningpoint of the oriented polymer comprising the web. A problem with theseoriented polymers is their poor heat sealability. Traditional orientedpolymer films are heat sealed by the entire film being thermally-weldedabove its melting temperature. This type of heat sealing by weldingresults in severe shrinkage and warping in the weld region. Welding alsodestroys the orientation in the weld area resulting in a weakened filmor web in this critical area.

Efforts to make oriented semi-crystalline films heat sealable havegenerally focused on providing a thin layer of a heat sealable polymeron the film outer surface by coextrusion, sequential extrusion orcoating. However these processes are problematic in terms ofmanufacturability of the film and adherence between the two layers. Theheat sealable layer being formed of a lower molecular weight, lowersoftening point and/or less crystalline polymer also typically reducesthe bulk tensile properties of the film. U.S. Pat. No. 4,247,591proposes coextruding a thin outer layer of a higher average molecularweight version of the bulk polymer so both layers are subsequentlyoriented. The film is then selectively heated in these thin outerlayers. The results reported allege an increase in joint strength ofabout 30 percent over single layer oriented films with a welded joint.Problems with this process include the need for careful selectiveheating to ensure that the heat seal remains primarily in the highmolecular weight outer layers. The process also would not be suited tothin films of less than about 5 mils(127 μm).

Also of concern with oriented films are the high gloss and low abrasionresistance of these films. A series of patents are directed at providingplastic strapping for industrial packaging use. The plastic strapping isformed from oriented polymeric films. The patents address the high glossand abrasion resistance problems of these oriented films. U.S. Pat. Nos.3,394,045 and 4,428,720 propose heating the oriented film to a fusiontemperature (e.g., about 475° F.(246° C.) for polypropylene) by a flameor heated chromed roll. The depth of treatment is about 1 mil(25.4 μm).The straps can then allegedly be used like conventional steel strappingto form crimped joints. However, this process is not well suited toproviding heat sealable films. The high temperature and long dwell timeof the treatment results in considerable oxidized species on the outersurface of the strapping, which is not a problem for crimped joints butwhich contaminates any heat seal joint. The high treatment temperaturewould also make manufacturability difficult for thin films due to thetendency of relatively thick melted polymer layers to adhere to rollersand associated machinery. U.S. Pat. No. 4,090,008 also reports that theabove patents are deficient in preventing dusting or edge fibrillationand proposes a process for sealing only the edges with a heat treatment.U.S. Pat. No. 4,451,524 addresses the same fibrillation problem andpurposes a subsequent orientation step following fusion of the surfacelayer (again about 1 mil(25.4 μm)).

U.S. Pat. No. 4,822,451 summarizes various prior art film surfacetreatments and their effects, including; corona treatment, plasmatreatment, sputter-etching, E-beam treatment, flame treatment, highintensity U.V. treatment and laser treatment. The object of thetreatment process discussed in this patent is to treat a very thinsurface layer of a film so that there is little or no chemical (exceptcrystalline structure) or textural changes in the film polymer on theouter surface. All the summarized prior art treatments result in achange in the texture and/or chemical nature of the polymer surfacesbeing treated. The treatment described is a high intensity, high fluencelaser (e.g., excimer laser) that when used with an appropriatesemi-crystalline polymer creates a, preferably, 20-250 nm thick layer oftreated polymer that is in a quasi-amorphous state. The quasi-amorphousstate is characterized by loss of short range crystallization, butretains a limited level of long range orientation that can be seen ifthe treated layer is recrystallized. This treatment requires suitablematching of the laser wavelength to the absorption characteristics ofthe polymer and does not create any texturing of the treated polymersurface which is desirable in many applications thereby limiting itsapplicability.

SUMMARY OF THE INVENTION

The present invention provides a thin (e.g., less than about 5 mils(127μm) heat sealable, oriented, semi-crystalline and thermoplastic articleor material such as a web, e.g., a film or film layer, and a method forits production. Heat sealability is provided by a thin heat sealablesurface layer of the same polymer and similar crystalline state as thebulk polymer of the web, e.g., film or film layer. The treated surfacelayer is characterized by a lack of oxidated (e.g., degraded) speciesand typically increased surface texture. The treated film isparticularly well suited for use as a pressure-sensitive adhesive (PSA)tape backing.

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1 is a schematic diagram of the treatment process of the invention.

FIG. 2 are Glancing Wide Angle X-Ray Diffraction traces (GWAX) (1.0°) ofthe film of Example 2 on both a treated and a non-treated face.

FIG. 3 are Glancing Wide Angle X-Ray Diffraction traces (0.5°) of thefilm of Example 2 on both a treated and a non-treated face.

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS

The present invention provides a process for formation of a thin heatsealable semi-crystalline surface layer on a semi-crystalline orientedpolymer article or web, e.g., an oriented film or film layer, and thearticle or web of that process. The process involves rapidly heating athin layer of the oriented polymer, on the outer surface of the articleor web, under heat and pressure to a temperature above the melting pointof the oriented semi-crystalline polymer by use of a heated texturedsurface, such as a heated roll for an oriented web. The heating step isof a duration sufficient to treat only a 1 to 15 micron thick layer ofthe oriented polymer outer surface.

The invention treated surface layers, or surface layer areas or regions,are characterized by a lack of oxygen containing degradation speciessuch as obtained by typical heat treatment processes, like thosedescribed in U.S. Pat. Nos. 3,394,045 or 4,495,124 or ablative processessuch as described in U.S. Pat. No. 4,417,948. Oxidized species arenotably absent in the invention treated surface layer as measured byelectron spectroscopy analysis (the treated surfaces typically measuredfrom 99 to 100 percent carbon) (ESCA)(XPS) and water contact anglemeasurements, which were typically high(measured to be 88 to 95°)compared to prior art treated surface layers (a lower contact angleindicates higher oxygen content based on the higher surface energy).

The process of the invention is exemplified and described with referenceto FIG. 1. Reference numeral 1 indicates an oriented thermoplastic filmsupplied by an unwind roller 2 and suitable idler roll(s) 3. The film 1is fed to a nip 6 formed between a heated textured roll 5 and a backingroll 4, either or both of which can be driven. The heated nip roll 5 istextured, such as a chrome plated sandblasted steel roll. The roll 5 canoptionally be provided with a release surface to prevent build-up ofhigh tack melted polymer on the heated roll 5. The roll 5 can be heatedby conventional means such as hot water or oil, electric resistance orinduction heating.

The surface temperature of roll 5 is controlled so as to have atemperature at least 5° C. above the film 1 oriented polymer melttemperature, preferably at least 30° C. for chromed rolls and generallyhigher for release coated roll surfaces. The nip contact surface area ofthe film 1 with the heated roll 5 is generally very small, from about 1to 10 mm, preferably 2 to 5 mm, however a larger contact area can beused if the film 1 speed is proportionally increased. The film 1 speedthrough the nip 6 is preferably at least 50 feet (15M) per minute, andmore preferably at least 75 feet (23M) per minute. The preferred contacttime between the film and the heated nip contact area is less than about20 milliseconds (ms) and preferably less than about 15 ms, down to 5 msand less. At contact times greater than about 20 ms the treated filmlayer(s) will have the tendency to oxidize and severely degrade thetensile properties of the film or film layer. This will lead to a filmthat will not heat seal adequately and may break in the nip. The abovedescribed preferred conditions are dependent to some degree on thepolymer that forms film 1. Polymers with different viscoelasticproperties, theological properties or thermal conductivity propertiesmay require more or less exposure to the heated roll 5. The preferredconditions described above are primarily with respect to isotacticpolypropylene and similar polymers, copolymers and blends.

The backing roll 4 and the heated roll 5 are set to provide a nippressure sufficient to ensure substantially continuous contact betweenthe film surface being treated and the heated roll 5 (a limited amountof small or microscopic non-contact points between the heated roll 5 andthe film 1 is not undesirable and may contribute to clean release of thefilm from heated roll 5). The pressure required to do this is generallyless than the pressure used in a conventional embossing treatment. Thehigh temperature of roll 5 lowers the viscosity of a surface layer ofpolymer on film 1 sufficient to allow limited viscous flow of the heatedpolymer into contact with heated nip roll 5 at low pressures. Pressuresas low as 0.2 to 10 pounds per linear inch (PLI) (0.09-4.56 kg perlinear cm) have been found to be sufficient. At nip pressures greaterthan 10 PLI, the film has a tendency to distort, creating edge creping.The backing roll 4 is preferably cooled to prevent heat buildup in thenip 6. Backing roll 4 can also be provided with a thin deformable orelastic coating (such as silicone rubber with a durometer hardness ofless than about 80 Shore A) to better ensure contact between the film 1surface and the textured heated roll 5.

Drive roll 7 drives a nip provided between roll 7 and roll 8, one ofwhich is preferably coated with a silicone rubber. Rewind roll 9 is alsodriven, possibly by drive roll 7.

The film 1 is a semi-crystalline polymer that has been subjected toorientation in at least one direction to provide non-isotropic behaviorin the film. This orientation is conventional and will not be describedhere.

The orientation and crystallization of the polymer in film 1 is retainedin the treated surface layer, however at lower levels, as is depicted inthe GWAX traces in FIGS. 2 and 3. The level of orientation retained inthe treated layer is generally low but still present. In the GWAX tracesof FIGS. 2 and 3 this retention of orientation is apparent by thedifferences in relative intensity for the two major peaks, which aregenerally of equal size if there is no orientation in the polymer layertested. Crystalline structure is retained to a considerable extent (upto 60 to 96%) as determined by GWAX intensity and patterns (0.5° and1.0° ). No new crystalline peaks are typically formed, indicating thelack of change in crystalline structure or the creation of a purelyamorphous polymer in the surface layer, as in U.S. Pat. Nos. 4,822,451or 3,394,045. The 0.5° Glancing Wide Angle X-Ray diffraction pattern(GWAX) generally will show retention of at least 5-10 percent of theuntreated face crystallinity, preferably at least 50 percent and up to70 to 95 percent.

The crystalline size of the treated surface layer polymer issignificantly reduced, coupled with the reduction in the overall degreeof crystallinity and orientation. This is apparent from the decrease insoftening point temperature of the treated surface polymer layercompared to the untreated bulk polymer of film 1. The lowering of thetreated surface layer polymer softening point is demonstrated bysignificant self-adhesion bond strength of treated films, at the treatedfilm surface layers, at heat seal temperatures 5° C., and more, belowthe melting or softening point of the untreated oriented polymer offilm 1. Films with treated surface layer(s) can exhibit self-adherencebond strength values at these lower heat seal temperatures, on the orderof or higher than the bond strengths obtained with the untreated filmwelded at or near its softening point. The treated film can therefore beheat sealed without effecting the orientation and crystallinity of theuntreated bulk polymer and without the associated loss in film strengthat the joint as caused by welding. Adhesion of the invention treatedfilm, at the treated surface layer, to other surfaces, such aspolyolefins and copolymers, is also increased at these lower heat sealtemperatures.

Although the crystalline structure of the treated surface layer isaltered by the rapid topical heating of the film to temperatures well inexcess of the melting point of the oriented polymer, the crystallinestructure and associated properties are not lost as in conventional heattreatment. Further, the invention treatment process limits thepenetration of the treatment to a surface layer having a thickness ofless than about 20 microns(μm), preferably less than 15 microns, suchthat the treated layer is less than about 50 percent of the total filmthickness and preferably less than 20 percent. This limits the loss ofthe orientated bulk polymer properties in the final treated film. Theinvention treatment has also been discovered to minimize polymerdegradation and the associated creation of oxidized species, either onthe film as treated, or by transfer of melted polymer to the texturedheat treatment roll and back to the film.

The provision of a textured surface on the heated roll 5 in contact withthe film 1 surface has been found to inhibit or prevent transfer ofmelted polymer to the roll, particularly with conventional chromedsurfaces. The texture depth (Ra) is generally at least about 10micro-inch (0.3 μm), and preferably about 20 micro-inch (0.5 μm), butless than 400 micro-inch (10.2 μm). Use of higher Ra or deeper texturedrolls can result in uneven treatment of the film while lower Ra valuerolls can result in film or polymer sticking to the roll. The use ofrelease agent coatings, resistant to the high temperatures of the roll,are also advantageous to prevent polymer adhesion with certain high tackpolymers. Suitable release treatments include Teflon™(polytetrafluoroethylene) and other fluorochemical coatings.

The texture on the heated roll 5 is at least indirectly transferred tothe surface layer of film 1 resulting in increased texturing andassociated at least in part with a reduction in percent gloss at 60°,down to 30% and less, preferably to 15% and less. The gloss generallycan be from 3 to 50%, however is preferably from 5 to 30%. The Ra valuesfor the textured treated surfaces range from 20 to 500 micro-inch(μinch) (0.5-12.7 μm), preferably from 50 to 400 μ inch (1.3-10.2 μm).Lower Ra values are not significant and higher Ra values are difficultto obtain while still obtaining effective continuous surface layertreatment at the desired thicknesses. A peak count of at least 50peaks/inch(20 peaks/cm) is desirable, with 100 to 400 (39-157 peaks/cm)being preferred for a textured surface (measured as defined below). Thehighest texturing and reduction in gloss are obtained with non-releasecoated (e.g., chromed) heated roll surfaces, however, suitable releasecoatings may have to be employed with some polymers to avoid sticking ofmolten polymer to the heated roll and still obtain preferred texturing.Surface texturing of the treated surface layer is often demanded foruses where high gloss is not desirable, such as certain adhesive tapebackings, or where the, e.g., film surface is coated. The inventionsurface texturing is sufficient to satisfy the texturing requirementsfor these typical uses, without the typical undesired chemicalmodification of the exterior surface layer, as one obtains with the heattreatments of U.S. Pat. Nos. 3,394,045 or 4,428,720 or the surfacetreatments summarized in Table 1 of U.S. Pat. No. 4,822,451.

The polymers suitable for the invention treatment are orientablethermoplastic polymers, generally semi-crystalline thermoplasticpolymers such as polyolefins (e.g., polypropylene or polyethylene),polyesters, polyamides and the like. The polymer need only be capable ofbeing heated to a suitable temperature above its melting point withoutsticking or transferring polymer to the heated roll at the highprocessing speeds of the invention process. Polyolefins are generallywell suited, particularly polypropylene and copolymers, to the inventionprocess without sticking to the heated roll. Certain polyesters,however, are of a higher tack when melted and tend to stick to theheated roll. Further, due to the relatively higher melt temperatures ofthese polyesters, conventional release agents generally cannot be usedon the roll without undergoing degradation.

Due to the treated surface layer thicknesses (below 10 microns in somecases) the process can be used to treat very thin film or fiber webs(e.g., below 5 mils (100 μm), down to 1 to 3 mils (25-75 μm), ifdesired, without effecting the bulk properties of the oriented polymerof film 1 to any significant extent. The texture level of the heatedtreatment surface on, e.g., roll 5 should be matched to the treatmentlayer thickness, as determined by treatment temperature and exposureduration, to ensure substantially continuous contact between the meltphase of the surface layer and the heated textured surface duringtreatment.

The invention described above with respect to FIG. 1 is applicable toother webs or articles or could be practiced by other means. Further,the invention is exemplified by the following examples which set forththe currently contemplated preferred embodiments.

EXAMPLES Example 1

This example describes a one to two mil (25-50 μm) thick film ofbiaxially oriented polypropylene (M.P. 170° C.) that was rapidly passedover a heated TEFLON™ polymer coated roller. The roller was heated to asurface temperature of 250° C. The film surface visually had a texturedappearance.

Example 2

This example describes a one mil (25 μm) thick film of biaxiallyorientated polypropylene (BOPP) polymer (M.P. 170° C.) that was passedover a heated TEFLON™ (DuPont 958-203) polymer coated (1.5 mil, 38 μm,thick, polished to 30-50 micro-inch, 0.8-1.3 μm, Ra) roller at a speedof 75 feet per minute (fpm) (23 m/minute). The roller was heated to asurface temperature of 260° C. The web contacted about 2-4 mm of theroll surface. The film's surface finish was measured to be 57 micro-inch(1.4 μm) Ra with 105 peaks/inch (41 peaks/cm).

Measured using a Surtronic 3 Profilometer, (available fromTaylor-Hosson, Leicester, England), #1502 stylus, long stroke, 50bandwidth.

This film was tested for its auto adhesion using a heat sealing pressset at 40 pounds/inch² (3Kg/cm²) and 1 second. This film was tested forits auto adhesion using a second. The first noted bond strength (t-peelASTM D1876-72) was at 300° F. (149° C.) and was about 3.4 pounds/inch(0.6Kg/cm²). An untreated film's first noted autoadhesion was at 340° F.(171° C.) and was about 0.3 pounds per inch (0.05 Kg/cm) using a 180degree peel test as described below.

Counterexample 3

A one mil thick film of biaxially oriented polypropylene (M.P. 170° C.)was treated by passing the film at a web speed of 30 fpm (9 m/min) overa course-finished plasma coated roll (Plasma Coatings Inc., #315),80-100 μ-inch (2-2.5 μm) Root Mean Squared (RMS) finish heated to atemperature of from about 280° C. to 290° C. with a roll outer surfacetemperature of from about 250° C. to 260° C. The web contacted about 2-4mm of the roll surface. The surface finish was measured to be 435micro-inch (11 μm) Ra with 75 peaks/inch (30 peaks/cm). The depth of thesurface treatment was viewed from an edge-on perspective of a ScanningElectron Microscope (SEM) and appeared to be close to the thickness ofthe film, or approximately 25 microns. This film retained little of thebulk orientation of the original film.

Example 4

The film of example 2 was treated using a grit-blasted, chromed steelroll (Ultra Plating, Inc., 70 micro-inch (1.8 μm) Ra, 200-300 peaks/inch(79-118 peaks/cm)) at a web speed of 150 fpm (46 m/mira) and surfacetemperatures of from about 190° to about 200° C. About 2-4 mm of theroll was contacted by the web. The thus treated film has a surfacefinish of 70 micro-inch (1.8 μm) Ra with 230 peaks/inch (91 peaks/cm).The depth of the surface treatment of the film cross-section wasmeasured by SEM to be about 4-5 microns. The percent gloss was measuredto be 15 using a Gardner Gloss meter at a 60° angle, which would beconsidered a matte finished film.

The film surfaces, treated and untreated, were measured forcrystallinity by GWAX as described in Physical Review Letters, 66(9), p1181-1184 (1991) with both faces tested along the same axis relative tothe orientation direction. At 1°, the treated layer had 22% lowercrystallinity than the untreated film face with 58% lower crystallinityat 0.5° GWAX. The GWAX peaks 110 [13.5°(2Θ)] and 040 and 130 [17 and18.5 (2Θ)] were also asymmetrical on both faces indicating crystallineorientation of the polymer at both faces. The Example 2 film wassimilarly tested and displayed 12% and 50% lower crystallinity of thetreated face at 1.0° and 0.5° respectively (See FIGS. 2 and 3 which showthe Example 2 scan traces where 21 and 31 are the untreated faces and 22and 32 are the treated faces for 1.0 degree and 0.5 degree,respectively. The traces are of intensity vs. 2-Theta.)

The textured face of this film was also laminated to a blown highdensity polyethylene film (2 mil (51 μm), Consolidated Thermoplastics)in a heat sealing press set at 30 pounds per inch² (2 Kg/cm²) and 300°F. (149° C.) for 1.5 seconds. The samples were anchored using a doublecoated tape and a rolldown of 4.5 lbs (2.1 Kg) and subjected to an 1800peel test at a peel rate of 12 inch/minute (30 cm/min), giving a peelforce of 250 grams/inch (0.98 Kg/cm). An untreated film, similarlylaminated to this same blown film, gave a peel force value of 10grams/inch (0.04 Kg/cm).

EXAMPLE 5

The film of Example 2 was treated by passing the film over agrit-blasted chromed steel roll (Ultra Plating, Inc., 50 micro-inch (1.3μm) Ra, 200-300 peaks/inch (79-118 peaks/cm)) at a web speed of 150 fpm(46 m/min) and surface temperatures of from about 190° to 200° C. About2-4 mm of the roll was in contact with the web. The treated thicknesswas measured by SEM and found to be from about 3 to about 7 microns. Thesurface roughness was measured to be 61 micro-inch (1.6 μm) Ra, 260peaks/inch (102 peaks/cm). The percent gloss, measured at 60°, was foundto be 14. This gave the film a matte finished appearance.

Example 6

The film of example 2 was treated by passing the film over agrit-blasted chromed steel roll (Ultra Plating, Inc., 35 micro-inch (0.9μm) Ra, 200-300 peaks/in (79-118 peaks/cm)) at a web speed of 200 fpm(61 m/min) and surface temperatures of from about 190° to 200° C. About2-4 mm of the roll was in contact with the web. The treated thicknesswas measured by SEM and found to be from about 3 to about 6 microns. Thesurface roughness was measured to be 54 micro-inch (1.4 μm) Ra, 260peaks/inch (102 peaks/cm). The percent gloss, measured at 60°, was foundto be 14. This gave the film a matte finished appearance. This film wasnot uniform due to sticking of the film to the roll surface which wasdue to the low Ra value of the heated roll.

Comparative Example 7

The film of example 2 was treated in a manner as taught in U.S. Pat. No.4,495,124. By passing the one mil biaxially orientated polypropylenepolymer film over the highly polished, chromed steel roll (UltraPlating, Inc., 8-10 micro-inch (0.2-0.26 μm) finish) at web speed of 30fpm (9 m/min) with a roll surface temperature of about 180° C. Nomaterial could be treated because the film stuck to the heated rollsurface in the nip. This dwell time is similar to the fastest dwelltimes described in the above patent. The process as described in thispatent may well be suited to thick, uniaxially oriented webs but was notfound suitable for treating thin, biaxially or uniaxially oriented websto provide heat sealable oriented material.

The various modifications and alterations of this invention will beapparent to those skilled in the art without departing from the scopeand spirit of this invention, and this invention should not berestricted to that set forth herein for illustrative purposes.

I claim:
 1. A process for forming a heat sealable surface layer orregion on an oriented film or film layer of crystalline orsemi-crystalline polymer comprising the steps of:(a) providing anoriented film or film layer of a crystalline or semi-crystallinepolymer. (b) contacting at least a region of one outer surface of saidoriented film or film layer with a heated textured surface at atemperature above the melting point of said oriented polymer for a timesufficient to treat a layer of said film to a thickness of no greaterthan 15 microns and at a pressure sufficient to ensure substantiallycontinuous contact between the film and the heated textured surface. 2.The process of claim 1 wherein the film is contacted with a heatedtextured roll with a backing nip at said pressure sufficient to ensuresubstantially continuous contact between the film and the heatedtextured roll.
 3. The process of claim 2 wherein the heated texturedroll has an Ra of at least 20 μ inch.
 4. The process of claim 3 whereinthe heated textured roll is coated with a release coating.
 5. Theprocess of claim 3 wherein the backing nip has a durometer hardness ofless than about 80 Shore A.
 6. The process of claim 3 wherein thebacking nip has a durometer hardness of less than about 80 Shore A andis coated with a silicone rubber.
 7. The process of claim 3 wherein thefilm is in contact with the heated roll for about 1 to 10 mm when thefilm is moving at at least 50 feet per minute.
 8. The process of claim 7wherein the film is moving at at least 75 feet per minute.
 9. Theprocess of claim 3 wherein the film is in contact with the heated rollfor 20 ms or less.
 10. The process of claim 2 wherein the film is incontact with the heated roll for 15 ms or less.
 11. The process of claim1 wherein the film is in contact with the heated roll for 5 ms or less.12. The process of claim 3 wherein the film is treated to a thickness ofat least 1 micron, said treated layer having the same, but lower,crystalline state as the untreated polymer.
 13. The process of claim 12wherein the treated region polymer has 5 to 95% less crystallinity thanthe untreated polymer.
 14. The process of claim 12 wherein the treatedregion polymer has 30 to 50% less crystallinity than the untreatedpolymer.
 15. The process of claim 1 wherein the heated roll temperatureis at least 5° C. higher than the melting point temperature of theuntreated film or film layer oriented polymer provided in step (a). 16.The process of claim 1 wherein the heated roll temperature is at least20° C. higher than the melting point temperature of the untreated filmpolymer.
 17. The process of claim 1 wherein the heated roll temperatureis at least 30° C. higher than the melting point temperature of the filmpolymer.